Eyepiece and telescope pairing
Celestron X-Cel LX 2.3mm in the Sky-Watcher Evostar 72ED: magnification and field
What the Celestron X-Cel LX 2.3mm does in the Sky-Watcher Evostar 72ED, worked from the published focal lengths and apparent field.
Field of view
ring = 0.33 degrees true
dot = 0.4 mm exit pupil
- Magnification
- 183x420 mm / 2.3 mm
- True field
- 0.33 degrees60 deg / 183x
- Exit pupil
- 0.4 mm72 mm / 183x
- Max useful mag
- 170xpublished
Computed optics
- Barrel match
- 1.25 in eyepiece in a 2 in focuser
Over-powered. At 183x this pair exceeds the published highest useful magnification of about 170x for the Sky-Watcher Evostar 72ED, so the image dims and softens without showing more real detail. Use a longer eyepiece.
Magnification is the telescope focal length divided by the eyepiece focal length: 420 mm divided by 2.3 mm is 183x. The true field of view is the eyepiece's 60 degree apparent field divided by that magnification, 0.33 degrees.
The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 72 mm over 183x, which is 0.4 mm. That makes this a high-power lunar, planetary and double-star setting.
The eyepiece to buy
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